It's different for game to game.
Some games suppots 1080i resolutions in ps2 & some native 640x480
if u want to get higher resolution possible for FFX.set 2x-4x in video plugin & see what best works
maybe u'r pc will struggle beause it needs high resources.
So start with 2x then higher

So, I should play with x3 native screens and not 1080p like I've been playing with to prevent crashes or anything? I played up to where Tidus meets Yuna (not completed yet though) and everything worked perfectly but for the fact that monsters and tidus fight backwards.